Patching the ACE/Server 4.1 replaces the aceclnt.dll in ace\prog with a new version that needs the ACE/Agent for Windows NT 4.3.

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Make sure you are running the latest ACE/Agent on the ACE/Server. Replace the aceclnt.dll in ace\prog with the one from the winnt/system32 directory, and then restart ACE/Server. If necessary Install the latest ACE/Agent and copy the aceclnt.dll file from the winnt/system32 directory to the ACE/Server ace/prog directory.